A photodiode is a type of photodetector capable of converting light into either current or voltage, depending upon the mode of operation. Many diodes designed for use specifically as a photodiode use a PIN junction rather than a p-n junction, to increase the speed of response. Sensor is a device that converts an optical signal into an electronic signal. Extra circuitry next to each photo sensor converts the light energy to a voltage. Additional circuitry on the chip may be included to convert the voltage to digital data. The signal performance is dependent on the photoreception. However, when the device is scaled down with trend, the photo diode surface is also reduced along with the shrinkage. Thus, the minimized area of the photodiode cannot offer good performance.